1. Field of the Invention
This invention relates to a waveguide type optical filter having wavelength selectivity, and more particularly to an optical module for wavelength division multiplexing using a waveguide type optical filter.
2. Description of the Prior Art
The techniques for the multi-wavelength transmission for optical fiber communication is very important for economizing the same communication. In the multi-wavelength transmission, an optical multi/demultiplexer is an essential device.
The conventional optical multi/demultiplexers include an optical multi/demultiplexer constructed by using an optical interference film filter ("Optical Communication Handbook" published by the Asakura Shoten, pages 325-331). The optical multi/demultiplexer using this optical interference film filter has excellent loss characteristics in a pass band and a loss band, and excellent pass band characteristics, and is going to be widely used. In this optical multi/demultiplexer, an optical interference film filter is vacuumevaporated on a glass plate, and this optical interference film filter-carrying glass plate is bonded to a glass block with an adhesive agent. However, it is necessary that an accurate axis-aligning operation be carried out during the bonding of such a filter-carrying glass plate to the glass block with an adhesive agent. When the adhesive agent is applied to the glass plate to a certain thickness, the angle of the glass plate bonded to the glass block becomes different. Therefore, it is necessary to adjust the position and angle of the glass plate while exciting the light. Moreover, the assembly-processing time is required excessively, and this makes it difficult to reduce the manufacturing cost. In addition, this optical multi/demultiplexer also requires the glass block to be lustered, and the size accuracy and the angle accuracy to be improved, so that the device becomes very expensive. The low mass productivity of the device is also a cause of its high price. If a light-emitting semiconductor device and a photo-detector are combined with this optical multi/demultiplexer so as to obtain a hybrid module for bidirectional transmission, much more time is required for assembly-processing the parts and adjusting the optical axis since the object module is a combination of separate parts. The price of such a product also becomes high.